The present invention relates to a coating composition and process for protecting small metallic parts from corrosion. More specifically, the present invention relates to an aqueous based organic rust preventative coating composition and process for protecting conversion coated steel fasteners or other small conversion coated steel parts.
Steel fasteners and other small steel parts are often employed in an environment which is conducive to corrosion, typically red rust. Rust is not only unsightly but it prevents good adhesion of paint or other coatings. Furthermore, rust will eventually destroy the steel fastener or part. In the case of fasteners which are employed to hold together portions of automotive vehicles or other products, it is particularly important to minimize their susceptibility to rust. The need for protecting steel surfaces from rust is, of course, well known and has been the subject of a considerable amount of research and development.
A conventional technique for protecting steel surfaces from rust involves contacting the steel surface with a solution containing phosphate ions to form a corrosion resistant, nonreactive phosphate complex coating on the steel surface. The steel surface is thus converted from a chemically active surface readily susceptible to oxidation and the coating thereon is known in the art as a "conversion coating." Following the application of a conversion coating to the steel surface, an after-treatment can be employed to further enhance corrosion resistance. Treatment with a dilute aqueous acidic solution of a chromium compound is a well known after-treatment. Still further rust prevention can be obtained by application of an organic top coat to the steel surface.
The present invention relates to a coating composition and process which provide excellent rust prevention to conversion-coated steel fasteners or other small conversion-coated steel parts when applied thereto. The composition of the present invention is an aqueous based composition, thus, avoiding the disadvantages associated with solvent based composition. In addition, the present composition enjoys good shelf-life, i.e. stability under conditions of normal storage, transportation and use. The composition and process of the present invention are particularly well adapted and effective to provide a rust preventative coating on fasteners and the like which are subjected to mechanical force such as threading during use.
Further understanding of the present invention will be had from the following disclosure wherein all parts and percentages are by weight unless otherwise indicated.